1. Field of the Invention
This invention relates to a telecommunication switching system, and more particularly to a telecommunication switching system which is suitable for use as an electronic switching system or a crossbar switching system.
2. Description of the Prior Art
An ordinary telecommunication switching system employs a matrix or matrixes for switching in a switching network. The matrix has theoretically or physically fixed numbers of inlets and outlets, and the ratio of the numbers of the inlets and outlets in the single matrix or the plural matrixes combined together is called the concentration ratio.
A variety of concentration ratios are required to comply with the particular construction of the telecommunication switching system used.
Conventional methods that have heretofore been employed are as follows:
(A) A matrix having a required concentration ratio is newly designed. For example, in the case of the concentration ratio being 3:2, a new matrix (1) is manufactured to have twelve inlets (2) and eight outlets (3), as shown in FIG. 1.
(b) Plural matrixes are combined together to obtain a matrix group having outlets, the number of which is an integral multiple of a required number of outlets. For instance, in the case of the concentration ratio 3:2, six matrixes (4), each having eight inlets (5) and eight outlets (6), are combined together to obtain a matrix group of which the number of inlets .times. the number of outlets is 24 .times. 16, as depicted in FIG. 2.
(c) A certain number of inlets are of no use. For example, in the case of the concentration ratio 3:2, two matrixes (7), each having eight inlets (8) and eight outlets (9), are combined together, and are operated as a matrix so that the number of inlets .times. the number of outlets is 12 .times. 8, with four inlets held redundant, as illustrated in FIG. 3.
(d) Two kinds of matrixes are combined together. For instance, in the case of the concentration ratio 3:2, a matrix (10) having four inlets (11) and eight outlets (12), and a matrix (13) having eight inlets (14) and eight outlets (15), are combined together to obtain a matrix group so that the number of inlets .times. the number of outlets is 12 .times. 8, as shown in FIG. 4.
The abovesaid method (a) is uneconomical and time-consuming. The method (b) has the following defects: In the case of applying the matrix group to a multistage switching network of more than one stage, an increase in the traffic capacity of the switching network is not in proportion to an increase in the number of cross-points, and a decrease in the traffic capacity per cross-point is inevitable, and since this matrix group has k (.gtoreq.2) links between each primary matrix and each secondary matrix, the link matching method must be changed. The method (c) is uneconomical because some inlets must be held redundant. The method (d) requires two kinds of matrixes, and hence is economically unfavorable in the preparation of spare parts and in the other maintenance. Besides, it is also possible to prepare two kinds of matrixes of the same number, for example, one kind having sixteen inlets and eight outlets, and the other having eight inlets and eight outlets. But this is not preferred because of unbalanced service between the matrixes of different kinds.
Further, in the case of hunting the outlets of the matrix, since it is desirable from the viewpoint of reliability that the cross points be used uniformly, all the outlets selectable by each inlet may be customarily hunted in accordance with a "random hunting" principle. However, when such outlet hunting principle is applied to the hunting of outlets of multiple connection adopted in this invention, the traffic characteristics of the second matrix group is markedly degraded as compared with the traffic characteristics of the first matrix group, with the result that required traffic characteristics cannot be obtained. These problems will become more apparent from the following detailed description of this invention.